Field of the Invention
The present invention relates to a receiving circuit of a controller area network, particularly to a receiving circuit with an ultra-wide common-mode input voltage range, which can receive a signal ranging between a maximum common-mode voltage and a minimum common-mode voltage.
Description of the Related Art
The controller area network (CAN) issued by International Standard Organization (ISO) (ISO-11898) is a communication system developed for European automobiles to transmit information in very harsh environments, integrating several in-vehicle controllers or computers to a network for sharing responsibilities and information, whereby to execute the demanded functions. The CAN bus is able to transmit information stably in harsh or instable electrical environments and usually applied to the control systems of various types of vehicles. The CAN bus adopts the two-wire differential technology and uses differential signals to transmit information. The common-mode signals on the two wires are maintained at a DC voltage, whereby only a very small amount of electromagnetic waves is emitted from the transmission lines, and whereby the CAN bus can transmit signals persistently while external common-mode signals interferes with the differential bus.
In a vehicular environment, great ground voltage shift exists between the ground terminals of different communication nodes. The maximum level of the ground shift voltage will be further increased by batteries with higher output voltage be applied in future vehicles. For example, the output voltage level of the batteries applied in traditional gasoline vehicles is 12V. However, the output voltage level of the batteries applied in modern electric vehicle has been increased to 48V for longer battery life currently. Therefore, the common-mode input voltage range of the CAN transceiver integration circuit must be improved continuously so as to normally receive information in the case that great ground voltage shift exists between the ground terminals of different communication nodes. Besides, in order to avoid electromagnetic emission (EME) from the communication network to interfere other functions of the vehicle, the common-mode signal of the CAN bus must be maintained at a fixed DC voltage and avoid any unnecessary high-frequency fluctuation on the common-mode signals during the circuit operation.
There have been many conventional technologies applied to the differential receiving circuit of the CAN transceiver. For an example, a U.S. Pat. No. 7,274,916B2 disclosed a differential receiving circuit and a method thereof. The conventional differential receiving circuit comprises a first voltage-current converter converting a voltage signal at a first input to a first current, a second voltage-current converter converting a voltage signal at a second input to a second current, and a current subtractor providing a differential current of the first current and the second current. For another example, a U.S. Pat. No. 7,567,105B2 disclosed a high-speed CAN receiving circuit with improved anti-electromagnetic interference ability, wherein the receiving circuit is connected with a resistor assembly among the power supply end, the ground end, the CAN high end and the CAN low end to attenuate the signals on the CAN bus. Next, the resistor assembly-attenuated signals are input to a front-end amplifier to amplify the reciprocal of the attenuation ratio of the resistor assembly. Thus, the intensity of the differential signal at the front-end amplifier output end is equal to the intensity of the differential signal on the CAN bus. The common-mode voltage at the front-end amplifier output end is attenuated to a range handleable by the comparator. Further, the front-end amplifier also outputs a common-mode voltage to a basic voltage generator for generating a reference voltage level to the comparator. Then, the comparator compares the signal output by the front-end amplifier and the reference voltage to determine the logics level of the received signal. For a further example, a U.S. Pat. No. 7,738,566B2 disclosed a circuit device for data transmission systems and an operating method thereof, wherein a resistor assembly is connected with the power supply end, the ground end, the CAN high end and the CAN low end to divide the voltages of the signals on the CAN bus and attenuate the common-mode signals to the range handleable by the rear-stage front-end amplifier, and wherein the output of the resistor assembly is electrically connected with a sets of front-end amplifiers which accepts the common-mode input voltage being limited by the power supply, whereby the range of the acceptable common-mode input voltage of the receiving circuit is increased.
All the abovementioned conventional technologies are used to improve the common-mode input voltage range of the receiving circuit of the CAN bus. However, each of them still has limitation in the input common-mode voltage range, not necessarily meet to the requirement of current CAN bus operation environment. For examples, in the U.S. Pat. No. 7,274,916, the highest common-mode input voltage is limited by the highest current driving capability of the transistors M0 and M3, ands the lowest common-mode input voltage is limited by the values of the currents of ICML and ICMH; in the U.S. Pat. No. 7,567,105, the common-mode input voltage range of the front-end amplifier is between (VCC−1.8)V and (−0.8) V; in the U.S. Pat. No. 7,738,566, the common-mode input voltage range of the front-end amplifier is between (VCC−1.1875)V and (−∞)V. Therefore, all the abovementioned conventional technologies respectively have their own limitations. Besides, in the U.S. Pat. No. 7,738,566 and U.S. Pat. No. 7,567,105, the common-mode voltage level of the CAN bus during recessive state is determined by the voltage divisions of the power supply voltage, and the voltage division is undertaken by the resistor assembly electrically connected with the power supply end, the ground end, the CAN high end and the CAN low end. However, the resistance values of the resistors are likely to deviate from the designed values in practical fabrication of chips. Thus, the common-mode voltage level of the CAN bus during the recessive state is likely to deviate from the common-mode voltage level output by the transmitter of the CAN transceiver integration circuit during the dominant state. Then, the common-mode signals of the CAN bus are likely to have high-frequency fluctuation, which causes EME to be increased during transceiver circuit operation.
Accordingly, the present invention proposes a receiving circuit with an ultra-wide common-mode input voltage range, which can be applied as the receiving circuit of a CAN transceiver integration circuit, to overcome the problems of the conventional technologies.